3Feb 28, 2009 Merlion hit by lightning A lightning bolt struck the Merlion statue at about 4.30pm yesterday.The national icon at One Fullerton facing the Singapore Riverlost part of its top left mane and is believed to have its right ear chipped.About 20 to 30 people nearby, including tourists, ran helter-skelter in the pouring rain when debris from the Merlion's head went flying.Some ran to safety in the nearby shops and cafes.The fragments fell onto the patio at One Fullerton and the Singapore River Cruise counter near the Merlion.Nobody was hurt.Eyewitness Ms Rina Toh, 17, a barista at The Coffee Bean and Tea Leaf at One Fullerton, said: 'I saw a bright Z-shaped lightning bolt, and it was a lot bigger than usual.'She was standing at the counter and could see the Merlion.
4What is Physics?Physics is the study of the natural world around us – from the very large, such as the solar system, to the very small, such as the atom.
5Physical Quantities, SI Units and Measurement In the quest to understand nature, scientists use physical quantities to describe the world around us.Physical Quantities, SI Units and MeasurementChapter 1
6At the end of this chapter… You should be able to:show understanding that all physical quantities consist of a numerical magnitude and a unitrecall the following base quantities and their units: mass (kg), length (m), time (s), current (A), temperature (K)use the following prefixes and their symbols to indicate decimal sub-multiples and multiples of the SI units: nano (n), micro (μ), milli (m), centi (c), deci (d), kilo (k), mega (M)
7At the end of this chapter… You should be able to:show an understanding of the orders of magnitude of the sizes of common objects ranging from a typical atom to the Earthdescribe how to measure a variety of lengths with appropriate accuracy by means of tapes, rules, micrometers and calipers, using a vernier scale as necessarydescribe how to measure a short interval of time including the period of a simple pendulum with appropriate accuracy using stopwatches or appropriate instruments
9Why do We Need to Measure Things? Let’s do this as a class…Work in groups of twoCompare the length between the elbow to the first finger tip.
10Why do We Need to Measure Things? Are they the same?
11Physical Quantities and SI Units Base QuantityName of SI unitSymbol for SI UnitLengthmetremMasskilogramkgTimesecondsElectric CurrentampereATemperaturekelvinKIntensitycandelacdAmount of Substancemolemol
12Physical QuantitiesA physical quantity when measured may be described in terms ofA numberIts unit of measurementactual length = m
13Physical QuantitiesWhat is your height?2 mquantityunit
14Physical QuantitiesMass – unit of measurement, kilogram (kg)
15Physical QuantitiesTime – unit of measurement, second (s)
16Physical QuantitiesWhat are some problems we might face in our daily lives if there are no standard measurements?
17Do You Know??? 1 400 000 000 m 1.4 Gm (gigametre) 0.0002 m Diameter of the SunThickness of a strand of hairmm1.4 Gm (gigametre)0.2 mm (millimetre)
18Prefixes for SI units 10 giga- G 10 mega- M 10 kilo- k 10 deci- d 10 FactorPrefixSymbol109giga-G106mega-M103kilo-k10-1deci-d10-2centi-c10-3milli-m10-6micro-10-9nano-n
19Prefixes Exercise 1 Express the following quantities in their respective SI unit.One kilometer =1000m or 103mOne microsecond =s or 10-6sOne centimeter =0.01m or 10-2mOne gram =0.001kg or 10-3kgFactorPrefixSymbol109giga-G106mega-M103kilo-k10-1deci-d10-2centi-c10-3milli-m10-6micro-10-9nano-n
20Prefixes Exercise 1 One miligram = 0.001g or 10-3g =10-6 kg FactorPrefixSymbol109giga-G106mega-M103kilo-k10-1deci-d10-2centi-c10-3milli-m10-6micro-10-9nano-nOne miligram =0.001g or 10-3g=10-6 kgOne millisecond =0.001s or 10-3sOne minute =60sOne hour =3600s
21What does SI units mean? Système International International System of Units
22Measurement of Length m metre The SI unit for length is ( )Other units for length:mmetremillimetre (mm), centimetre (cm), kilometre (km)
23Accuracy of Instruments Measurement of LengthRangeSuitable InstrumentsAccuracy of InstrumentsSeveral metres (m)Several centimetres (cm)Between 1cm to 10cmLess than 2 cmMeasuringTape0.1 cm(or 1 mm)Metre/Half-metre Rule0.1 cm(or 1 mm)VernierCalipers0.01 cm(or 0.1 mm)MicrometerScrew Gauge0.001 cm(or 0.01 mm)
24Measurement of Length Metre rule: Measuring Tape - Length of classroom, car, corridorMetre rule:Length of desk, book
25Measurement of Length Parallax Error What is Parallax Error? It is the error which arises due to incorrect positioning of the eye.2.7 cmcorrect3.0 cmwrongcm123
26Measurement of Length Parallax Error How do we avoid Parallax Error? Always place the eye vertically above the mark being read. ORPlace the eye in level with the mark being read.3.0 cmwrong2.7 cmcorrectcm123
27Vernier Calipers French scientist Pierre Vernier(1580-1637) Accuracy: 0.01 cm (or 0.1 mm)
28How to read off the Vernier Caliper? 11mm0.7mmmmMeasured ValueReading = 11 mm mm = 11.7 mm
29Vernier Calipers Its structure and its application The inside jaws is used to measure internal diameter of test-tube, ring etc.In main scale, reading = 1.90 cmin vernier scale, reading = 0.01 cmthe actual reading = 1.91 cm
30Vernier Calipers Its structure and its application The outside jaws is used to measure small length, diameter of test-tube etc.main scale reading = 4.20 cmvernier scale reading = 0.06 cmActual reading = 4.26 cm
46Micrometer Screw Gauge Zero Error (Micrometer Screw Gauge)Positive Zero Error+0.02 mmZero Error = mmIf the observed reading = 2.37mm, thenActual measurement = Observed reading – Zero error= mm= mm+0.02(+0.02)2.35
47Micrometer Screw Gauge Zero Error (Micrometer Screw Gauge)Negative Zero ErrormmZero Error = mmIf the observed reading = 2.37mm, thenActual measurement = Observed reading – Zero error= mm= mm- 0.03(- 0.03)2.40
48Measurement of Time Two types: SI unit of time: second, s Stopwatches are used to measure short intervals of time.Two types:Digital stopwatchAnalogue stopwatchSI unit of time: second, s
49Accuracy of Instruments Measurement of TimeInstrumentsUsageAccuracy of InstrumentsWatch/Clockhrs, mins, secAnalogue Stopwatchmins, secDigital StopwatchAtomic Clockabout s-Pendulum ClockRadioactive decay clockthousand of years1 s0.1 s0.01 s
50Measurement of Time Watch/Clock used for measuring long intervals of timemost modern watches depend on the vibration of quartz crystals to keep time accuratelythe energy that keeps these crystals vibrating comes from a small batterymany watches still make use of coiled springs to supply the needed energy
51Measurement of Time Stopwatch (Analogue/Digital) Digital Stopwatch A stopwatch is used to measure short intervals of time.stopwatches (analogue and digital)Digital Stopwatchaccuracy = 0.01 sAnalogue Stopwatchaccuracy = 0.1 s
52Measurement of Time Atomic Clock Atomic clock also work on oscillation.The big difference between a standard clock in your home and an atomic clock is that the oscillation in an atomic clock is between the nucleus of an atom and the surrounding electrons.They even keep time better than the rotation of the Earth and the movement of the stars.Without atomic clocks, GPS navigation would be impossible, the Internet would not synchronize, and the position of the planets would not be known with enough accuracy for space probes and landers to be launched and monitored.
53Measurement of Time Pendulum Clock clocks make use of a process which is a regularly repeating motion (oscillations), such as the swing of a pendulumsuch oscillations are very regular so period is regularmost modern clocks depend on the vibration of quartz crystals to keep time accuratelyin clocks that are wound up, elastic potential energy is stored in coiled springs
54What is a pendulum?A small object suspended by a piece of string or tread is called a simple pendulum.The distance from the centre of the pendulum bob to the point of suspension is called the length of the pendulum.One complete to and fro movement of the pendulum is called an oscillation.The time taken for one complete oscillation is called the period.The distance between the rest position of the pendulum and the extreme point of its oscillation is called the amplitude.
55Diagram of a Pendulum Amplitude Length of Pendulum From B to C A C B OscillationFrom A to B to Cand back to B to A
57Finding the Period of a Pendulum To find the period:1. Take the total time for 20 oscillations.Why 20?2. Repeat 2 more times.3. Calculate the average time for 20 oscillations.4. Divide by 20 to obtain the period.
58What Affects the Period of a Pendulum? Mass?Amplitude?Length?
59Simple Pendulum When the length increases, the period increases. When the length decreases, the period decreases.When the mass of the bob increases/decreases, there is no effect on the period.
60Simple PendulumWhen the amplitude of the bob increases/decreases, there is no effect on the period.When the same experiment is done on the moon, the period increases.
61Pendulum ExerciseThe time taken for a pendulum to swing from rest position A to B is 0.8s. What is the time taken for the pendulum to make 20 oscillations?